Insert molding process has a problem that the process would be complex compared with an ordinary molding process using resin alone, since an insert member needs to be placed in a cavity of a mold prior to filling with resin. To solve the problem and to automate the molding process, several insert molding methods have already been proposed.
The most typical one is an insert molding method using a rotary turntable. In this insert molding method, one stationary mold and two to four movable molds are used to obtain a single type of molded product. In the method, a stationary mold is mounted on a main body of the molding machine while the remaining two to four movable molds are placed on the rotary turntable. While the turntable is rotated, placement of an insert member, confirmation of the placement, filling of resin and molding to shape, and ejection of a molded product will take place in order. Even if the operation process for molding is simplified to the greatest possible extent, the turntable must be provided with at least a stage for placing an insert member and removing a molded product, and a stage for molding the product into shape by filling resin. Thus, at least two movable molds and the turntable for placing these molds thereon are needed to obtain a single type of molded products.
Consequently, in the case of the insert molding method using the rotary turntable, the weight of the overall equipment becomes large and the turntable increases in overall machine size, thereby giving rise to a problem that the location for installation is largely limited. Also, since two or more movable molds are needed to obtain a single type of molded products, the manufacturing cost of the molds is high, causing a high unit cost of products. Further, it is difficult to control the temperature of two or more movable molds to exactly an equal level, causing a problem of dispersion of product quality due to the difference in operating conditions of the movable molds, even when the same products are molded continuously.
In addition, since a plurality of movable molds are placed on the turntable and are positioned relative to the stationary mold, each time the table is rotated, the positional relationship between the movable and stationary molds cannot always be aligned perfectly. In some cases, the stationary and movable molds are scratched by being dragged against each other or slightly displaced from each other, possibly adversely affecting the accuracy of products or shortening the lives of the molds.
An insert molding method using a linear sliding table, instead of the rotary turntable, has also been proposed but it differs from the above-described method only in that a plurality of movable molds make rectilinear movements and not circular movements. With this method, the installation space for the molding machine can be saved to some degree, however the aforementioned problems associated with the insert molding method using the rotary turntable still exist.